Pathogens are all possible objects (microorganisms, substances, etc.) that may cause illnesses. Where humans are concerned, one refers to human pathogens. Pathogens that trigger diseases in plants are known as phytopathogens.

Prokaryote (procarya, procaryote; Gr. pro = before and karoun = nut, nucleus), also called prokaryonte, are cellular organisms possessing no distinct nucleus. Their cell type is referred to as a protocyte. Since the time when all cellular organisms were reorganized into three domains, the domains of the bacteria and the archaea, all prokaryotes, are viewed together and the term has lost much significance as a result.

Proteomics encompasses proteome research. This covers the entirety of all proteins present in a cell under predefined conditions and at a specific point in time. Contrary to the (more static) genome, the proteome is (highly) dynamic and for this reason changes in its qualitative and quantitative protein content as a result of changed conditions (environmental factors, temperature, gene status, agent administration etc.).

Protozoa is an old-fashioned term, as this group is not based on common ancestors. Protozoa are single-celled eukaryotes (organisms whose cells have membrane-bound nuclei) that commonly show characteristics usually associated with animals, most notably mobility and heterotrophy.